Check and reseat all the connectors. That pin has had a long journey and those connectors aren't the best.

there should be 2 trim pots on the sound board. One is labelled speech. wind it back and forth a few times and see if it then works.

http://www.pinrepair.com/bally/squawk.htm

Have the connectors been re-pinned? That era of Bally you really should rebuild ALL of the .100 Molex connectors for reliability.
Very tedious work, but rewarding once your problems go away.

http://www.pinrepair.com/connect/

I have a Vector incoming and that will be my first job of it hasn't already been done. That and the EPROM sockets.

When I got my Embryon it was missing a lot of the speech. It worked, but only some words. It turned out the sound board was not from an Embryon and it was jumped wrong. Right board, wrong settings. These are the soldered in jumpers on the board. So have a look at the manual and go over the jumper leads very carefully. If that is it, it's a quick fix. People just miss it because who solders jumpers? Those crazy 80s.

And it was a guy on here named Vector that found and fixed it for me.

How many flashes do you get from the LED on the Squawk and Talk board? You should be getting 6 flashes, I think; maybe 5.

Good call. I think there's some misinformation floating around out there regarding the jumpers on this one. If I recall correctly, the bad information is specifically about whether jumper EE should be in place. I've got an Embryon and can check on that if the OP needs.

By the way, excellent purchase. I would love an Embryon.

Had mine since 2010, it's not going anywhere...

Missing input can cause wrong sound / speech calls.

Start simple stuff first before heating up the iron. Check the four/five encoded inputs are proper and making it through the 4049 to the PIA/sound generator.

The schematic sheet clearly labels the test points.

Not many of them over here in the UK.

Wow I have the same exact problem. Alltek board only some speech. 3 ball and Embryon functional. Recapped squawk and talk. Checked jumpers and reseated the connectors.

For what it's worth, Embryon uses the speech far less than Centaur or Eight Ball Deluxe. The only things that are actually said regularly, to my recollection, are "Embryonic incubator functional" when you start the game, "Embryon" when you add a letter, "Flip save energized" when you get A and B, and "Life support activated" when you light the lock.

Have you actually run the sound board through test mode?

Excellent. Glad to hear it.

It is a great pin. Mine lasted more than 4 years here, which is an eternity for a pin.